Pioner Josè Manuel, Pierantozzi Enrico, Coppini Raffaele, Rubino Egidio Maria, Biasci Valentina, Vitale Giulia, Laurino Annunziatina, Santini Lorenzo, Scardigli Marina, Randazzo Davide, Olianti Camilla, Serano Matteo, Rossi Daniela, Tesi Chiara, Cerbai Elisabetta, Lange Stephan, Reggiani Carlo, Sacconi Leonardo, Poggesi Corrado, Ferrantini Cecilia, Sorrentino Vincenzo
Department of Biology, University of Florence, Florence, Italy.
Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy.
J Gen Physiol. 2025 Jul 7;157(4). doi: 10.1085/jgp.202413696. Epub 2025 May 14.
Obscurin is a large muscle protein whose multiple functions include providing mechanical strength to the M-band and linking the sarcomere to the sarcoplasmic reticulum. Mutations in obscurin are linked to various forms of muscle diseases. This study compares cardiac function in a murine model of obscurin deletion (KO) with wild-type (WT) in vivo and ex vivo. Echocardiography showed that KO hearts had larger (+20%) end-diastolic and end-systolic volumes, reduced fractional shortening, and impaired ejection fraction, consistent with dilated cardiomyopathy. However, stroke volume and cardiac output were preserved due to increased end-diastolic volume. Morphological analyses revealed reduced sarcoplasmic reticulum volume, with preserved T-tubule network. While myofilament function was preserved in isolated myofibrils and skinned trabeculae, experiments in intact trabeculae revealed that Obscn KO hearts compared with WT displayed (1) reduced active tension at high frequencies and during resting-state contractions, (2) impaired positive inotropic and lusitropic response to β-adrenergic stimulation (isoproterenol 0.1 μM), and (3) faster mechanical restitution, suggesting reduced sarcoplasmic reticulum refractoriness. Intracellular [Ca2+]i measurements showed reduced peak systolic and increased diastolic levels in KO versus WT cardiomyocytes. Western blot experiments revealed lower SERCA and phospholamban (PLB) expression and reduced PLB phosphorylation in KO mice. While action potential parameters and conduction velocity were unchanged, β-adrenergic stimulation induced more frequent spontaneous Ca2+ waves and increased arrhythmia susceptibility in KO compared with WT. Taken together, these findings suggest that obscurin deletion, in adult mice, is linked to compensated dilated cardiomyopathy, altered E-C coupling, impaired response to inotropic agents, and increased propensity to arrhythmias.
obscurin是一种大型肌肉蛋白，其多种功能包括为M带提供机械强度以及将肌节与肌浆网连接起来。obscurin的突变与多种形式的肌肉疾病有关。本研究在体内和体外比较了obscurin缺失（KO）小鼠模型与野生型（WT）小鼠的心脏功能。超声心动图显示，KO心脏的舒张末期和收缩末期容积更大（增加20%），缩短分数降低，射血分数受损，这与扩张型心肌病一致。然而，由于舒张末期容积增加，每搏输出量和心输出量得以保留。形态学分析显示肌浆网容积减少，而T小管网络保留。虽然在分离的肌原纤维和脱膜小梁中肌丝功能得以保留，但在完整小梁中的实验显示，与WT相比，Obscn KO心脏表现出：（1）在高频和静息状态收缩时主动张力降低；（2）对β-肾上腺素能刺激（0.1μM异丙肾上腺素）的正性肌力和变时性反应受损；（3）机械恢复更快，提示肌浆网不应期降低。细胞内[Ca2+]i测量显示，与WT心肌细胞相比，KO心肌细胞的收缩期峰值降低，舒张期水平升高。蛋白质印迹实验显示，KO小鼠中SERCA和受磷蛋白（PLB）表达降低，PLB磷酸化减少。虽然动作电位参数和传导速度未改变，但与WT相比，β-肾上腺素能刺激在KO中诱导更频繁的自发性Ca2+波并增加心律失常易感性。综上所述，这些发现表明，成年小鼠中obscurin缺失与代偿性扩张型心肌病、E-C偶联改变、对正性肌力药物反应受损以及心律失常倾向增加有关。
